1. Field of the Invention
This invention relates to a roll for a radial thread-rolling head.
2. Description of the Related Art
In a radial thread-rolling head which has two or three rolls fitted with a thread-forming profile, such rolls are supported in a radially adjustable relationship. The thread-forming profile, as viewed in a circumferential direction, has a flattened area, a thread entry portion, a thread calibrating portion, and a thread exit portion. For reasons of forming and reasons of the torque to be applied by the machine, the aforementioned portions extend over a certain angle. Thus, the flattened area will usually extend over an angle of about 40.degree., the entry portion over an angle of 160.degree., the calibrating portion over an angle of 90.degree., and the exit portion over an angle of 70.degree.. The length of the calibrating portion usually is such as to correspond to a multiple of the circumferential length of the work to be formed.
It is by means of such a radial thread-rolling head that a thread is formed into a work over a restricted length. The rolls, when in their initial position, have a rotational position such that the flattened areas face each other. In this position of the rolls, the work may be inserted in the thread-rolling head. The rolls which are released by hand or automatically by the machine tool are automatically advanced radially towards the work so that the work, while being rotated by the machine tool, is capable of carrying the forming rolls along. The rolling operation will be completed after a single rotation of thread-forming rolls.
The thread-forming rolls are rotated by frictional engagement between the work and thread-forming rolls, and a spring mechanism is tensioned, and a clutch will be locked in place upon completion of the rolling operation so that the thread-forming rolls will release the work again.
Such a thread-rolling head or the forming rolls for such thread-rolling heads are known, for example, from DE 39 30 131 C1 or the Fette company publication "Rollsysteme".
Fortunately, rolls are of a certain axial length. This cannot be changed any more for a given version of a rolling head. On the other hand, what occurs in a number of applications is that the thread-forming roll is only utilized over a restricted axial area. This area will wear with time whereas the rest of the area remains usable, but is not used because of its position.
Therefore, it is an object of the invention to create a forming roller for a radial thread-rolling head, which is particularly useful in efficiently forming short threaded portions, but permits to be utilized completely.